Morphine is a narcotic pain reliever widely used to treat moderate to severe pain. It is generally thought that morphine acts as an agonist at the g-opioid receptor primarily and also the κ- and δ-opioid receptors of the central nervous system. By acting on one or more of these receptors, morphine can cause analgesia and anesthesia as a result of a receptor-mediated central action on pain perception. In addition to analgesia and anesthesia, morphine can provide widely diverse effects including alterations in mood, euphoria and/or feelings of relaxation, dysphoria, drowsiness, decreased gastrointestinal motility, respiratory depression, nausea, vomiting and alterations of the endocrine and autonomic nervous system.
Morphine has been used for a variety of clinical indications. Some examples of such indications include analgesia for treatment of acute and chronic pain due to, for example, cancer or post-operative surgery, anesthesia during surgery and to allay anxiety during acute pulmonary edema. Several delivery routes have been utilized for administering morphine. These routes include oral, rectal, parenteral (injectable) and buccal administration.